The present invention generally relates to fuel-fired heating appliances and, in a preferred embodiment thereof, more particularly relates to a fuel-fired, forced draft furnace having a specially designed self-cooling draft inducer fan.
In a forced draft fuel-fired heating appliance, such as a gas-fired air heating furnace, combustion products from a heat exchanger into which burner flames are injected are exhausted (after a substantial amount of heat is extracted from the combustion products by supply air passed exteriorly over the heat exchanger) from the heat exchanger by a draft inducer fan. A draft inducer fan of conventional construction and operation typically has a housing with an inlet opening formed on an inboard side thereof and mounted over a hole in a center panel portion of the furnace which forms a wall of the furnace housing portion in which the heat exchanger is disposed in the path of supply air being flowed through the furnace housing for heating therein.
An impeller wheel within the inducer fan housing is rotated by an electric motor carried by the housing and projecting outwardly from its outboard side, to draw spent combustion products into the fan housing and then discharge them to a flue structure operatively coupled to the outlet of the inducer fan. To cool the draft inducer fan motor, first and second small auxiliary cooling fans are typically connected to the drive shaft of the draft inducer fan. The first cooling fan is coaxially coupled to the inducer fan drive shaft between the electric motor and the inducer fan housing and functions, during operation of the inducer fan, to direct a cooling stream of air against the inboard shaft end bearing. The second cooling fan is coaxially coupled to the inducer fan drive shaft outboard of the electric motor and functions, during operation of the inducer fan, to direct a cooling stream of air against the motor windings and the outboard shaft end bearing.
This conventional arrangement of two auxiliary cooling fans associated with a draft inducer fan carries with it several well known problems, limitations and disadvantages. For example, this multi-fan arrangement undesirably adds to the operating noise level of the overall draft inducer fan assembly. Moreover, the previous necessity of using three fans in the overall draft inducing structure adds to the cost, complexity and space requirements for such structure. Additionally, the cooling air flow used to cool the inboard motor shaft end bearing can be deflected from the inducer fan housing against the adjacent fuel burner structures in a manner undesirably disrupting their flame patterns.
As can readily be seen from the foregoing, a need exists for an improved draft inducer fan structure that eliminates or at least substantially reduces these problems, limitations and disadvantages typically associated with conventional self-cooling draft inducer fan assemblies of the type generally described above. It is to this need that the present invention is directed.